This invention relates to vehicle test beds, and more particularly, relates to a surface coating for the rollers in use in such vehicle test beds.
In many cases, it has been found to be more convenient to use a test bed to test a vehicle's performance than to test it on the road. Vehicle test beds usually have at least one pair of spaced parallel rollers for driving engagement with at least one wheel of a motor vehicle to be tested. Such test beds may be used for a number of purposes including, but not limited to, the following: (1) testing of the vehicle's brakes by driving at least one of the rollers against the brakes; (2) using the vehicle brakes to decelerate the rollers when they are (a) freely rotating or (b) when at least one of the rollers is connected to a high inertia such as a fly wheel (the rollers may, of course, have sufficient inherent inertia in some cases); and (3) checking the vehicle's power or torque characteristic against speed. In this case, at least one of the rollers is connected to a brake such as an eddy current brake.
It will be appreciated that the surface of the rollers must be sufficiently rough to prevent any appreciable degree of slip between the rollers and the vehicle's wheel or wheels. In order to obtain a sufficient degree of roughness on the surface of the rollers, various techniques have been developed.
In some cases, the rollers have been manufactured from steel with a knurled or otherwise roughened surface. Such surface finishes have been found to be satisfactory in many respects. However a problem arises in that after a period of use, the knurled or roughened surface wears or becomes polished to such a degree that a substantial and undesirable amount of slip between the wheels and the rollers takes place.
In other cases, the rollers have been coated. It is known, for example, that the roller may be coated with concrete or flame sprayed with stainless steel. In so coating a roller, two problems are encountered.
The first problem is again the wearing smooth of the coating. The second problem involves what is generally characterized as the "burst speed" of the coating.
As a coated roller is rotated, centrifugal force is exerted on the coating. The "burst speed" is the speed at which a coating will shatter due to centrifugal stress.
The centrifugal force or stress which a coating can withstand depends upon its ultimate tensile strength. The ultimate tensile strength of concrete is quite low. A concrete roller, therefore, cannot be used in a relatively high speed device.
A coating comprising stainless steel particles flame sprayed onto the roller has a sufficiently high ultimate tensile strength, but it is subject to relatively rapid abrasion. As the coating wears smooth, slippage of course will occur, resulting in invalid test data.